If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Here's why the 2-Channel "H" is the deal of the century

Here are a couple of chassis shots that I recently took of my 2-Channel "H:"

It takes an amazing amount of "in chassis" handwork to build a 2-Channel compared to a modern production amp like those manufactured by Mesa Engineering. All of the pots, jacks, switches, lamps, and tube sockets have to be physically mounted to the chassis by hand. The boards are hand-populated outside of the chassis before being installed and hand-wired to the pots, jacks, switches, and tube sockets with flying leads. The the leads on the components that are directly attached to tube sockets, pots, and jacks are bent by hand and hand-soldered in place. Trust me; it takes a skilled person to build this amp because it would squeal like a pig if built by a low-skill employee.

The red and black jacks in the back are bias test points. The potentiometer mounted below the test points is the bias pot (Mesa does not even include a bias pot on their amps on their amps, which means that one is stuck using Mesa tubes or modifying the bias supply if one does not wish to risk a possible over-dissipation-related failure). The little cylindrical-shaped components that are wired between the black jack and the two red jacks are 1-Ohm resistors. What these resistors do is convert what would normally be a current reading to a voltage reading. Unlike power transistors, power tubes operate at high DC voltages (hundreds of volts) and low DC currents (millamps). When we draw current through a resistor, we develop a voltage drop that can be measured. This voltage drop is equal to the current being drawn through the resistor multiplied by the resistor's resistance value. Because the resistors have a value of 1-Ohm, the voltage reading in millivolts (a millivolt is equal to 10-3 volts) is equal to the current drawn in milliamps (a milliamp is equal to 10-3 amps). The reason why Doug and most amp designers who provide test points use the "voltage = current" test method is because it allows a service technician to check the amount of quiescent current drawn by the amp without having to break the cathode-to-ground connection. Normally, a service technician would have to insert his/her meter in series with each power tube cathode and signal ground to able to check the amount quiescent current that is being drawn by each power tube.

If one looks on the right-hand side of the second photo, one sees a bunch of wires that are bolted to the chassis. These wires are signal grounds. This grounding technique is known as "star grounding." Star grounding keeps the heavy loads imposed on the circuit by the power stage from flowing through the preamp signal grounds. If power stage current is allowed to flow through the preamp signal grounds, it can modulate the low-level stages in the preamp, resulting in hum or noise being injected into the preamp. It also greatly reduces or completely eliminates the possibility that a ground loop will creep into a design. A ground loop occurs when a circuit is grounded in more than one place. Ground loops are also a source of hum.

I paid $1.3K for my 2-Channel head at Experience last year (yes, that was a show-only price). Here's what one gets from Mesa Engineering for $1.3K:

Mesa Express 5:25

I know that I tend to target Mesa Engineering more than other amp companies. However, Mesa is held out as the gold standard of the amp world, so they are fair game when comparing build quality. There is absolutely no comparison between the 5:25 and the 2-Channel “H” from a build point of view. The 5:25 is designed to be assembled by low-level workers from a collection of PCBs that are mostly populated by pick-and-place machines. A few components are placed by hand before each PCB is sent through a wave soldering machine.

Here's a video that documents the Mesa PCB build process:

Mesa has not always used this type of construction. The Mark Series amps required much greater skill to build.

Mesa Mark III

As one can see, the Mark III, while still PCB-based, is not an everything on a PCB amp. All of the critical components are chassis mounted with flying leads. The Mark III required skill to build (this model was built when "Handbuilt in Petaluma" was more than just a slogan).

In closing, anyone who is attending Experience this year should plan to set aside a few minutes to meet with Doug and his team. The amp shop may not be as sexy as the rest of the factory, but these guys are turning out a quality product for a more than fair price when one considers that PRS amps are truly hand-built. Yes, the other models are more expensive, but that’s because many of the other amps use ridiculously expensive components. I guarantee that anyone who visits the PRS amp shop after viewing the video that I linked above will come away with a new appreciation for the Maryland-made PRS amps.

Note: There have been many revisions to the 2-Channel “H” to reduce noise and/or improve performance. My amp is a first generation pre-phase inverter master volume 2-Channel "H" (a.k.a. Rev. B). Earlier 2-Channel "H" amps had a master volume that was located after the phase inverter. For those who are curious, a phase inverter is a circuit that takes a signal as input and outputs an in-phase signal plus a signal that is 180-degrees out of phase with the input signal (i.e., a mirror image of the input signal). A phase inverter is necessary when coupling a preamplifier to a push-pull power stage. A phase inverter may or may not provide signal gain. A post-phase inverter master volume takes advantage of signal gain within a phase inverter circuit (usually a circuit known as a “Schmitt splitter”) to add an additional gain stage that can be overdriven before the master volume. Phase inverter distortion is a big component of the classic “dimed” Marshall tone.

Well Mark......I rarely understand the technical aspects of your posts....although I do appreciate the time and effort you put into your attempts to educate us.

that being said...well, of course that explains why my "H" sounds so damn good.

Now Mark...perhaps you can answer a non-related question. For awhile, I was running my combo "H" (and also my HXDA) into cabinets that were not matched. for example, I had the "H" going into an extension cab that was rated at 8 Ohms, even though the combo speaker is rated at 16 (I have subequently matched the ohm ratings correctly, but I digresss).

What is the "danger"..what are the pitfalls....of running a combo amp into an extension rated at a different ohm rating? And, along the same lines, what are the "hazards" of running a head into 2 cabinets, 1 at 16 ohms and the other rated 8 ohms. BTW...when I mismatched the 16 and 8 ohm speakers/cabinets, I set the overall ohm level at "8". I did not hear any differences at other settings, but that is irrelevant...I lack the auditory acuity to pick up the more subtle tonal variations.

I was under the impression that only the introductory run of H amps were hand wired in this manner?????

That aside, I'm failing to understand the point here. Sure, it's hand wired but what matters in the end is the sound. I hold PRS guitars in high esteem, like all of you. Their venture into higher gain amplifiers, on the other hand, is still years of revisions away from being on par with a Mesa or other higher gain boutique amp makers. The gain characteristics of the H and the SE amps are just pure fizz and shrill. I was appalled at how bad the H sounds, and its a quite obvious Marshall type knockoff. I know a statement like that won't be popular here but PRS really should stick to lower gain vintage type amps, which they seem to excel at. The H can't even really hold a candle to the Mesa Express series.... which so happens to actually be lower in price.

I was under the impression that only the introductory run of H amps were hand wired in this manner?????

That aside, I'm failing to understand the point here. Sure, it's hand wired but what matters in the end is the sound. I hold PRS guitars in high esteem, like all of you. Their venture into higher gain amplifiers, on the other hand, is still years of revisions away from being on par with a Mesa or other higher gain boutique amp makers. The gain characteristics of the H and the SE amps are just pure fizz and shrill. I was appalled at how bad the H sounds, and its a quite obvious Marshall type knockoff. I know a statement like that won't be popular here but PRS really should stick to lower gain vintage type amps, which they seem to excel at. The H can't even really hold a candle to the Mesa Express series.... which so happens to actually be lower in price.

Sorry to contradict....but my "H" blew away my Mark 1....as a matter of fact, my MDT and HXDA and my "H" blew away any Mesa I had ever owned. Of course, that is purely subjective. And is not relevant to this thread.

I think that the main point that Em7 consistently tries to make in his original post is not the concept of tone, which is subjective, but rather the type of build and resultant ease of repair. Apparently, the current PRS hand-built amps are much easier to repair and are much more reliable than Mesa's PCB circuitry..at least, that is what I am able to take away from his posts with my extremely limited capacity to comprehend his knowledge. I'll leave the rebuttal to a more knowledgeable individual, and await Em7's reply/

QUOTE=Drew;19149]I was under the impression that only the introductory run of H amps were hand wired in this manner????? [/quote]

No, all of the 2-Channels are hand-wired.

That aside, I'm failing to understand the point here. Sure, it's hand wired but what matters in the end is the sound.

I hold PRS guitars in high esteem, like all of you. Their venture into higher gain amplifiers, on the other hand, is still years of revisions away from being on par with a Mesa or other higher gain boutique amp makers.

The 2-Channel "H" isn't a super-saturated modern amp. It is merely a more focused and modern sounding version of the more vintage sounding 2-Channel "C." The difference between the two amps is like the difference between a JCM 800 with 6550s installed in the power stage and a JCM 800 with EL34s installed in the power stage.

The gain characteristics of the H and the SE amps are just pure fizz and shrill. I was appalled at how bad the H sounds, ... I know a statement like that won't be popular here but PRS really should stick to lower gain vintage type amps, which they seem to excel at. The H can't even really hold a candle to the Mesa Express series.... which so happens to actually be lower in price.

The 2-Channel "H" is anything but shrill and fizzing sounding in these two videos:

I will agree that the lead channel on the SEs needs to be re-voiced. However, the 2-Channel "H" sounds very good when used at stage volumes. One cannot approach the 2-Channel "H" like one approaches an Express. The 2-Channel "H" requires a more holistic approach to setup and more from the person holding the guitar. One cannot dime the preamp on the lead channel, set the master to one, and expect the amp to sound good. If one opens up the master on the lead channel, the 2-Channel "H" sounds anything but shrill. The 2-Channel "H" sounds best when the power amp is allowed to breath. On the other hand, the Express 5:50 is capable of decent low-volume gain tones, but leaves a lot to be desired when turned up. The power and output transformers on the 2-Channel are the proper size for a 50-Watt guitar amp. The output transformer on a 5:50 is the size of a Deluxe Reverb output transformer. The low -3dB down point for the Deluxe Reverb transformer is around 150 Hertz at 15 Watts, which means that it is incapable of reproducing the low "E" on a standard-tuned guitar at 15 Watts, let alone 22 Watts (the frequency of the low "E" on a standard-tuned guitar is approximately 82 Hertz). The output transformer on the Express 5:50 does not stand a chance of being able to reproduce the low "E" string at the amp's claimed 50-Watt power level.

and its a quite obvious Marshall type knockoff

Marshall did not invent the circuit that is behind the Marshall sound. They cloned the Fender 5F6-A Tweed Bassman, and performed step-wise tweaks to the circuit over the years. The 2-Channel "H" is also derived from Fender tweed circuits from the late fifties. Doug got his start in the amp world by working on and restoring tweed amps.

Every tube guitar amp on the market falls into one of three basic amp families; namely, the Fender tweed family (derived works are usually based on the 5F6-A Tweed Bassman), the Fender blackface family (derived amps are usually based on the AB763 circuit), and the Vox family. Every manufacturer puts their own spin on guitar amp designs that were created in the fifties and sixties. With Mesa, the Mark Series and the budget lines (Studio, DC, Nomad, F, and Express) are derived from the Fender AB763 blackface circuit. The Recto is derived from the Fender 5F6-A Tweed Bassman circuit. The Dual Rectifier is basically a 100W 5F6-A Tweed Bassman with more gain stages and selectable equalization networks, which, using your logic, would make the Recto a Marshall clone because Marshall was the first amp company to create a derived work from the 5F6-A circuit as well as the first amp company to add additional gain stages to the 5F6-A circuit.

Well Mark......I rarely understand the technical aspects of your posts....although I do appreciate the time and effort you put into your attempts to educate us.

that being said...well, of course that explains why my "H" sounds so damn good.

Now Mark...perhaps you can answer a non-related question. For awhile, I was running my combo "H" (and also my HXDA) into cabinets that were not matched. for example, I had the "H" going into an extension cab that was rated at 8 Ohms, even though the combo speaker is rated at 16 (I have subequently matched the ohm ratings correctly, but I digresss).

What is the "danger"..what are the pitfalls....of running a combo amp into an extension rated at a different ohm rating? And, along the same lines, what are the "hazards" of running a head into 2 cabinets, 1 at 16 ohms and the other rated 8 ohms. BTW...when I mismatched the 16 and 8 ohm speakers/cabinets, I set the overall ohm level at "8". I did not hear any differences at other settings, but that is irrelevant...I lack the auditory acuity to pick up the more subtle tonal variations.

Doc:

You are good as long as the parallel impedance is not less than half or more than twice the selected impedance on the amp. You should always pick the closest match to the parallel impedance.

The problem that one encounters when running different impedance cabs is uneven power distribution due to uneven current distribution. Often, the results are not what one expects. In your case, the 8-ohm cabinet will receive 2/3rds of the current, which means that 2/3rds of the power is being diverted to the 8-ohm cabinet.

I was under the impression that only the introductory run of H amps were hand wired in this manner?????

That aside, I'm failing to understand the point here. Sure, it's hand wired but what matters in the end is the sound. I hold PRS guitars in high esteem, like all of you. Their venture into higher gain amplifiers, on the other hand, is still years of revisions away from being on par with a Mesa or other higher gain boutique amp makers. The gain characteristics of the H and the SE amps are just pure fizz and shrill. I was appalled at how bad the H sounds, and its a quite obvious Marshall type knockoff. I know a statement like that won't be popular here but PRS really should stick to lower gain vintage type amps, which they seem to excel at. The H can't even really hold a candle to the Mesa Express series.... which so happens to actually be lower in price.

Drew, I like me some Mesas just fine, in fact, just had a Mark V in my studio, but honestly, the H amp sounds great. It's different from what you're used to, obviously, but it sure isn't fizzy or shrill. I'd suggest revisiting it and maybe trying some different settings.

What I'm using now is the HX/DA and I highly recommend it. To each his own however; I have nothing bad at all to say about Mesa amps, I like them and have had several, going back 20 years. And some day I'll get another one!

I think that the main point that Em7 consistently tries to make in his original post is not the concept of tone, which is subjective, but rather the type of build and resultant ease of repair. Apparently, the current PRS hand-built amps are much easier to repair and are much more reliable than Mesa's PCB circuitry..at least, that is what I am able to take away from his posts with my extremely limited capacity to comprehend his knowledge. I'll leave the rebuttal to a more knowledgeable individual, and await Em7's reply/

You are correct. For me, a tube amp has to be robustly built because I do not know how long I am going to own it. PCB-based amps have a finite shelf life with respect to repair. Manufacturer-only parts such as power amp PCBs are only available for a finite amount of time after an amp model has been discontinued. Unlike a hand-wired amp, a power tube failure that takes out a power tube socket also generally takes out the PCB on which the socket is mounted. The amp is repairable as long as the manufacturer still has spares. Beyond that point, one has to resort to cannibalizing other amps for parts.

Here’s what happens when a PCB-based tube amp suffers a catastrophic power tube failure:

If that amp hand been hand-wired, or at least had chassis mounted power tubes that were connected to the board via flying leads, the repair would have been limited to replacing the tube socket, which would have been a much cheaper and more timely repair.

Drew, I like me some Mesas just fine, in fact, just had a Mark V in my studio, but honestly, the H amp sounds great. It's different from what you're used to, obviously, but it sure isn't fizzy or shrill. I'd suggest revisiting it and maybe trying some different settings.

What I'm using now is the HX/DA and I highly recommend it. To each his own however; I have nothing bad at all to say about Mesa amps, I like them and have had several, going back 20 years. And some day I'll get another one!

WOW!! What a discussion... Like many of you, I have played through many amps over the years. Mesa, Marsall, VOX, Fender, Peavey, EVH, etc. They are all good amps. but as someone mentioned above your tone is a very subjective subject. But when Em7s post, I read that for the money, the build quality of PRS amps is excellent.

I have also played through a ton of PRS amps, Mine and some prototypes in Doug's lair. Some are not for me and some really get me excited. My Original Sewell is one of the best sounding amps I have ever played through. The MDT is great to... I was never blown away by the old Plexi tones so the HX/DA is not for me (but it is still a great amp).. my amp of choice is a 2 Channel C. I love the clean channel and the Lead channel is everything I'd hoped for over the years. I will not gig without it..

As for PRS Amps and Doug Sewell. You will not find a more responsive team. I have bothered Doug more than I am would like. but he has always been there.. The team down in Maryland are amazing to work with and extemely friendy.

my amp of choice is a 2 Channel C. I love the clean channel and the Lead channel is everything I'd hoped for over the years. I will not gig without it..

The 2-Channel "C" is built to the same standard as the 2-Channel "H." After all, the 2-Channel "C" was the basis for the 2-Channel "H."

Here's a 2-Channel "C" that was on a bench in the amp shop at Experience 2010:

As for PRS Amps and Doug Sewell. You will not find a more responsive team. I have bothered Doug more than I am would like. but he has always been there.. The team down in Maryland are amazing to work with and extemely friendy.

I would like to believe that the amp shop is currently at the point where PRS was when Paul and his team started to build guitars on Virginia Avenue. However, in reality, the amp shop is closer to 33 West Street in process maturity. We are truly living in the golden age of PRS amps. At some point, Doug and his team will have to adopt volume-oriented build techniques to keep pace with demand. Thatís what has happened to every other major amp manufacturer over time.

Let's examine Marshall's build process through the years. From the cabinet to the chassis to the turret board, the very first Marshalls were completely hand-built. At this point in the company's history, Marshall was basically a "boutique" amp company. Ken Bran, Dudley Craven, and Jim Marshall were personally involved in the construction of the amps.

Early JTM 45

Marshall switched over to using a steel chassis in 1967.

1968 JMP model 1959 "plexi" 100W Super Lead

Marshall switched over to using a metal faceplate in 1969; however, the amps remained hand-wired through 1973. In 1974, Marshall migrated all of the components that were mounted on the turret board to a printed circuit board (PCB). While not as desirable on the vintage market, the early PCB-based amps are robustly built. All of the critical components are chassis-mounted and connected to the PCB via flying leads.

1975 JMP model 1987 "metalface" 50W Lead

In the mid-eighties, Marshall started to migrate the remaining chassis-mounted circuitry to printed circuit boards in order to reduce build cost and increase output. One has more than likely noticed that there are two different styles of JCM 800 from the eighties. The amps with the vertical input jacks are built using the same techniques as the 1975 JMP shown above. The amps with horizontal input jacks are the first Marshall amps to have PCB-mounted pots and jacks. These amps were the beginning of the end for Marshall quality. Except for the JMP/ JCM 800 re-issues and hand-wired models, modern Marshall amps are everything-on-a-PCB amps.

I wish the 2 Channel H came in rackmountable as it is soooooo close in size to fitting. I would love to use it with my Fractal instead of just a poweramp. Power AND tone? Yes please.

interesting. I work for a band called O Rappa and we are preparing a new set with 2 x 100 watt "H" amps and the Axe FX 2. I am doing the first programming with a 50 watt "H" amp.Fractal &amp; PRS por aduayer, no Flickr

interesting. I work for a band called O Rappa and we are preparing a new set with 2 x 100 watt "H" amps and the Axe FX 2. I am doing the first programming with a 50 watt "H" amp.Fractal & PRS por aduayer, no Flickr

Nice man! Hows the rig going to work? Are you using the Fractal for effects only or are you going to A/B it with the PRS heads?

Nice man! Hows the rig going to work? Are you using the Fractal for effects only or are you going to A/B it with the PRS heads?

We'll use just the power of the PRS amps. Effects and pre will be from the Fractal. We're doing this way, so in case anything happens with the Fractal, we still have the option to use the pre from the PRS amps.

We'll use just the power of the PRS amps. Effects and pre will be from the Fractal. We're doing this way, so in case anything happens with the Fractal, we still have the option to use the pre from the PRS amps.

Sounds like a great plan! In my live rig I run output 1 of the fractal with cab sims direct to out to FOH and output two without cab sim's to my power amp into my cab for that extra boom

Maybe you can help me convince Doug Sewell at Experience to make a PRS rackmounted power amp! haha

Thanks for this thread!! I owned a PRS SE head and 2x12 cab. I was within the return window at my local PRS dealer and was able to return the SE gear and order a 2 Channel H 1x12 combo. Having now owned both amps, I can say with EXTREME confidence that the 2 Channel H destroys the SE in terms of tone, musicality, and build quality. Night and day difference. It's worth spending some extra cash for the 2 Channel H My new favorite amp!